1. Field of the Invention
The present invention relates generally to the configuration, deployment, and operation of pressure control equipment used in drilling subsea wells. More particularly, the present invention relates to an independently controlled backup blowout preventer assembly that can assist containment of a subsea wellbore in the event of a failure or malfunction of the primary subsea blowout preventer stack, the primary blowout preventer control system, the subsea/surface communication conduits, the surface rig systems or combinations thereof.
2. Background of the Technology
In most offshore drilling operations, a wellhead at the sea floor is positioned at the upper end of the subterranean wellbore lined with casing, a blowout preventer (BOP) stack is mounted to the wellhead, and a lower marine riser package (LMRP) is mounted to the BOP stack. The upper end of the LMRP typically includes a flex joint coupled to the lower end of a drilling riser that extends upward to a drilling vessel at the sea surface. A drill string is hung from the drilling vessel through the drilling riser, the LMRP, the BOP stack, and the wellhead into the wellbore.
During drilling operations, drilling fluid, or mud, is pumped from the sea surface down the drill string, and returns up the annulus around the drill string. In the event of a rapid invasion of formation fluid into the annulus, commonly known as a “kick”, the BOP stack and/or LMRP may actuate to help seal the annulus and control the fluid pressure in the wellbore. In particular, the BOP stack and LMRP include closure members, or cavities, designed to help seal the wellbore and prevent the release of high-pressure formation fluids from the wellbore. Thus, the BOP stack and LMRP function as pressure control devices.
For most subsea drilling operations, the BOP stack and LMRP are operated with a common control system physically located on the surface drilling vessel. However, damage to the drilling vessel from a blowout, ballast control issue, collision, power failure, etc., may result in damage and/or complete loss of the control system and/or the ability to operate the BOP stack. In such cases, the subsea BOP stack and LMRP may be rendered useless, even if intact, because there is no readily available means to actuate or operate them.
Accordingly, there remains a need in the art for systems and methods to help control a subsea well in the event of a blowout. Such systems and methods would be particularly well-received if they offered the potential to remotely control and seal the well independent of the primary control system housed on the surface drilling vessel.